A CeCoOx Core/Nb2 O5 @TiO2 Double-Shell Nanocage Catalyst Demonstrates High Activity and Water Resistance for Catalytic Combustion of o-Dichlorobenzene

A series of catalysts with different core-shell structures has been successfully prepared by a hydrothermal method. They consisted of CeCoO_x @TiO₂ (single shell), CeCoO_x @Nb₂ O₅ (single shell) and CeCoO_x @Nb₂ O₅ @TiO₂ (double shell) core-shell nanocages and CeCoO_x nanocages, in which CeCoO_x was the core and TiO₂ and Nb₂ O₅ were shells. The influence of the core-shell structure on the catalytic performance of o-dichlorobenzene was investigated by activity, water-resistance, and thermal stability tests as well as catalyst characterization. The temperatures corresponding to 90 % conversion of o-dichlorobenzene (T₉₀ ) of CeCoO_x , CeCoO_x @TiO₂ , CeCoO_x @Nb₂ O₅ , and CeCoO_x @Nb₂ O₅ @TiO₂ catalysts were 415, 383, 362 and 367 °C, respectively. CeCoO_x @Nb₂ O₅ exhibited excellent catalytic activity, mainly owing to the special core-shell structure, large specific surface area, abundant activity of Co³⁺ , Ce³⁺ , Nb⁵⁺ , strong reducibility, and more active oxygen vacancies. It can be seen that the Nb₂ O₅ coating can greatly improve the catalytic activity of the catalyst. In addition, due to the protective effect of the TiO₂ shell on CeCoO_x , CeCoO_x @Nb₂ O₅ @TiO₂ catalysts exhibited outstanding thermal and hydrothermal stability for 20 hours. The T₉₀ of CeCoO_x @Nb₂ O₅ @TiO₂ was slightly lower than that of CeCoO_x @Nb₂ O₅ , but it had higher stability and hydrothermal stability. Furthermore, possible reaction pathways involving the Mars-van-Krevelen (MvK) and Langmuir-Hinshelwood (L-H) models were deduced based on studies of the temperature-programmed desorption of O₂ (O₂ -TPD), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance FTIR spectroscopy (DRIFTS) characterization.

Catalytic combustion of VOC on sandwich-structured Pt@ZSM-5 nanosheets prepared by controllable intercalation

A sandwich-structured Pt@ZSM-5 nanosheets (Pt@PZN-2) was fabricated by controllable intercalating Pt nanoparticles between ZSM-5 single-layer sheets via electrostatic adsorption with ammonium ions in diquaternary ammonium surfactant, and the following calcinations. Pt clusters (ca. 4.3 nm) confined between nanosheet layers (thickness of ca. 2.9 nm) exhibits better dispersion and higher thermal stability even after high-temperature treatment, while the Pt clusters also served as pillars which well protected the inter-layers mesopores. Catalytic combustion of toluene (a model compound of large molecules VOCs) shows catalytic activity of Pt@PZN-2 is significant higher than that of Pt-loaded nanosheet ZSM-5 zeolite prepared by conventional impregnation (Pt/ZN-2). For example, the temperature at 98% toluene conversion of Pt@PZN-2 is only 176 °C which is 24 °C and 34 °C lower than that of Pt/ZN-2 and bulky ZSM-5 supported Pt by impregnation (Pt/CZ-500), respectively. Meanwhile, Pt@PZN-2 also gives 100% toluene conversion for more than 360 h at 230 °C with a higher metal stability. The good performance of Pt@PZN-2 was attributed to the high accessibility and enhanced diffusion of the bulky reactant to active site confined in the stable inter-layer mesopores resulting from the pillar of Pt nanoparticles.

Microfibrous-Structured Pd/AlOOH/Al-Fiber for CO Coupling to Dimethyl Oxalate: Effect of Morphology of AlOOH Nanosheet Endogenously Grown on Al-Fiber

We report a green, template-free, and general one-pot method of endogenous growth of free-standing boehmite (AlOOH) nanosheets on a 3D-network 60 μm-Al-fiber felt through water-only hydrothermal oxidation reaction between Al metal and H₂O (2Al + 4H₂O → 2AlOOH + 3H₂). Content and morphology of AlOOH nanosheets can be finely tuned by adjusting the hydrothermal oxidation time length and temperature. Palladium is highly dispersed on such AlOOH endogenously formed on Al-fiber felt via incipient wetness impregnation method and as-obtained Pd/AlOOH/Al-fiber catalysts are checked in the CO coupling to dimethyl oxalate (DMO) reaction. Interestingly, Pd dispersion is very sensitive to the thickness (26-68 nm) of AlOOH nanosheet, and therefore the conversion shows strong AlOOH-nanosheet-thickness dependence whereas the intrinsic activity (TOF) is AlOOH-nanosheet-thickness independence. The most promising structured catalyst is the one using a microfibrous-structured composite with the thinnest AlOOH nanosheet (26 nm) to support a small amount of Pd of only 0.26 wt %. This catalyst, with high thermal-conductivity and satisfying structural robustness, delivers 67% CO conversion and 96% DMO selectivity at 150 °C using a feed of CH₃ONO/CO/N₂ (1/1.4/7.6, vol) and a gas hourly space velocity of 3000 L kg^-1 h^-1, and particularly, is very stable for at least 150 h without deactivation sign.

Vapor-phase transport synthesis of microfibrous-structured SS-fiber@ZSM-5 catalyst with improved selectivity and stability for methanol-to-propylene

Microfibrous-structured SS-fiber@HZSM-5 catalyst prepared by cost-effective and high-efficiency VPT method delivers remarkable improvement in selectivity and stability for the MTP reaction due to the improved diffusion in zeolite shell.

High sintering-/coke-resistance Ni@SiO2/Al2O3/FeCrAl-fiber catalyst for dry reforming of methane: one-step, macro-to-nano organization via cross-linking molecules

A thin-felt, microfibrous-structured Ni@SiO₂/Al₂O₃/FeCrAl-fiber catalyst was fabricated by one-step, top-down macro–micro–nano organization, displaying tremendous potential for dry reforming of methane.